The present invention relates, in general, to a parking brake assembly for use in a railway vehicle braking system and, more particularly, this invention relates to a spring applied parking brake assembly for use in a railway vehicle braking system which is activated by the absence of air in the railway vehicle braking system and, still more specifically, the present invention relates to a spring applied parking brake assembly for use in a railway vehicle truck mounted brake assembly.
As is generally well known in the railway industry, when railway cars are taken out of a train and parked at a siding, or yard, the hand brake or parking brake on at least some of these cars is applied as a precaution against unwanted or unexpected movement of the cars. A typical railway car hand brake system normally consists of an apparatus for manually applying and biasing one or more brake shoes against the tread of one or more wheels of the railway car by either turning a hand wheel or pumping a ratchet handle on a hand brake mechanism attached to the railway car.
As illustrated in FIG. 3, in truck mounted braking systems, the hand brake mechanism is normally either a cast or stamped metal gear housing usually attached to an outside end wall of the railway car. Such hand brake mechanism has a rotatable chain drum therein which can be rotated by turning the hand wheel to wind a brake chain onto the chain drum.
The other end of the brake chain normally extends through the bottom of the gear housing and is interconnected with a cable, or other linkage such as a hand brake lever, to the brake beam which carries the brake shoes such that winding of the brake chain onto the chain drum will apply tension to the brake chain and linkage as necessary to draw the interconnected brake shoes against the tread surfaces of adjacent railway car wheels and, accordingly, apply the hand brake as intended.
A disadvantage of this prior art type hand brake arrangement is that an operator must be certain that the handwheel is turned at least a sufficient amount to ensure that the parking brake is engaged. Also, the possibility exists that the operator may forget to apply the brake altogether, which could result in unexpected movement of the railway car while parked at the siding or yard. Furthermore, operation of the handwheel requires exerting a considerable amount of physical force from an awkward position. This, in turn, makes the hand brake difficult to apply.
Briefly, the invention comprises a casing which is mounted on or within the braking system, typically alongside the air cylinder. This casing contains a spring member and a piston assembly, both of which are mounted for longitudinal movement within the casing. One end of the spring member contacts or is capable of pushing against an inside surface of the casing. The opposite end of the spring member is associated with the piston assembly such that the piston assembly moves in accordance with movement of the spring member. The piston assembly includes a piston rod associated therewith which also moves in accordance with movement of the spring member. The piston rod is attached to or is associated with the force transfer lever of the braking system such that longitudinal movement of the piston rod causes this force transfer lever to rotate and apply a force to at least one force transmitting member in the vehicle braking system to initiate a brake application.
Air pressure from the pneumatic braking system causes the spring to remain in compressed condition while the railway car is in position within the train consist. Upon removal of this railway car from the train and consequently from the pneumatic braking system, the spring automatically extends to its natural position so as to initiate the braking sequence.
The invention also includes an arrangement or system for installing the spring applied parking brake assembly within a railway vehicle braking system. This arrangement comprises a tubular member mounted for longitudinal movement within the casing. The tubular member is also associated with the piston assembly and the spring member and moves in accordance with movement of the piston assembly and the spring member. The casing includes an opening at one end and the tubular member can extend through this opening when the piston assembly and spring member are moved in a direction so as to compress the spring member. A holding means is provided for holding the portion of the tubular member which extends through the opening in place so that the spring member is held in the compressed position which causes the spring applied brake assembly to be in a deactivated position. Consequently, the spring applied parking brake assembly may be held in this deactivated position during installation within the railway vehicle braking system. Additionally, this holding means may be employed to hold the spring applied parking brake assembly in a deactivated position if for any reason one would desire that the parking brake on the car remain deactivated after removal of the car from the pneumatic braking system of the railway vehicle.
It is an object of the present invention to provide a spring applied parking brake assembly for a railway vehicle braking system which is an ergonomic alternative to the currently used manually activated hand brake assemblies.
Another object of the present invention is to provide a spring applied parking brake assembly which is particularly applicable to a truck mounted braking system.
Still another object of the present invention is to provide a spring applied parking brake assembly which may be used to replace the currently used manually activated handwheel hand brakes.
It is a further object of the present invention to provide a spring applied parking brake assembly for a railway vehicle braking system which is activated by the absence of air in the braking system ensuring that the parking brake is activated as soon as the car has been removed from the air brake system of the train.
Yet another object of the present invention to provide a spring applied parking brake assembly for a railway vehicle braking system which, if necessary, may be mechanically deactivated.
It is yet a further object of the present invention to provide a spring applied parking brake assembly for a railway vehicle braking system which by virtue of being automatically activated upon the removal of the car from the air brake system of the train will eliminate the possibility of operator error in applying the parking brake.
It is another object of the present invention to provide an arrangement or system for installing the spring applied parking brake assembly within a railway vehicle braking system.